Computer simulation of some dynamical properties of the Lorentz gas

We carried out molecular dynamics simulations of a Lorentz gas, consisting of a lone hydrogen molecule moving in a sea of stationary argon atoms. A Lennard-Jones form was assumed for the H₂-Ar potential. The calculations were performed at a reduced temperatureK ^* =kT/_{H 2–Ar} = 4.64 and at reduced densities ^*= _{Ar Ar} ³ in the range 0.074–0.414. The placement of Ar atoms was assumed to be random rather than dictated by equilibrium considerations. We followed the trajectories of many H₂ molecules, each of which is assigned in turn a velocity given by the Maxwell-Boltzmann distribution at the temperature of the simulation. Solving the equations of motion classically, we obtained the translational part of the incoherent dynamic structure factor for the H₂ molecule,S _tr(q, ). This was convoluted with the rotational structure factorS _rot(q, ) calculated assuming unhindered rotation to obtain the total structure factorS(q, ). Our results agree well with experimental data on this function obtained by Egelstaffet al. At the highest density ( ^*=0.414) we studied the dependence ofS(q, ) on system size (number of Ar atoms), number of H₂ molecules for which trajectories are generated, and the length of time over which these trajectories are followed.     

Measurement of the g-Factor of the 27− High-Spin Isomer State of 152Dy

The g-factor of the 27⁻ isomer state of ¹⁵²Dy has been measured using the Time-Integral Perturbed Angular Distribution (TIPAD) method. The high-spin states of ¹⁵²Dy have been populated by ¹⁴¹Pr(¹⁶O,p4n)¹⁵²Dy reaction at E = 115 MeV from the AVF cyclotron at CYRIC. The paramagnetic correction factor of Dy ions in Pr has been determined to be 4.2(5) by the Time-Differential Perturbed Angular Distribution (TDPAD) measurement of the 21⁻ state of ¹⁵²Dy. As a result, the g-factor of the 27⁻ isomer state of ¹⁵²Dy has been obtained to be +0.09(5). This shows the smaller value than the expected one of +0.39 deduced from a fully aligned configuration of π(h _11/2 ²) ⊗ ν(f _7/2 ² h _9/2 i _13/2).     

Frequency combinations in the magnetoresistance oscillations spectrum of a linear chain of coupled orbits with a high scattering rate

The oscillatory magnetoresistance spectrum of the organic metal (BEDO)₅Ni(CN)₄. 3C₂H₄(OH)₂ has been studied up to 50 T, in the temperature range from 1.5 K to 4.2 K. In high magnetic field, its Fermi surface corresponds to a linear chain of quasi-two-dimensional orbits coupled by magnetic breakdown (MB). The scattering rate consistently deduced from the data relevant to the basic α and the MB-induced β orbits is very large which points to a significant reduction of the chemical potential oscillation. Despite of this feature, the oscillations spectrum exhibits many frequency combinations. Their effective masses and (or) Dingle temperature are not in agreement with either the predictions of the quantum interference model or the semiclassical model of Falicov and Stachowiak.     

平行因子分析法在太湖水体三维荧光峰比值分析中的应用

以太湖水样三维荧光光谱数据为例,提出在采用平行因子分析法(PARAFAC)处理后的荧光数据中提取荧光峰强度计算荧光峰比值进行水环境分析评价的方法,较直接在水样原始荧光谱图中获取的荧光峰强度更加准确客观。天然水体中各水样间由于受荧光团复杂多样性等因素的影响,某类荧光物质荧光峰的激发发射波长位置并不是固定不变的,就同一水样而言各类荧光峰之间的相互重叠干扰也将影响到荧光峰强度和位置的准确判断。而在PARAFAC模型各因子中提取相应荧光峰值可以保证各水样间同类荧光物质荧光峰在同一位置又有效减弱同一水样中各类荧光物质荧光峰之间的相互干扰,更加高效准确的利用荧光峰比值进行水环境分析。区域差异性分析时水样因子得分比值的区域变化与原始荧光峰比值变化趋势是一致的。     

Application of fast Pade approximation in simulating photonic crystal nanocavities by FDTD technology

The exact calculation of mode quality factor Q is a key problem in the design of high-Q photonic crystal nanocavity. On the basis of further investigation on conventional Pade approximation, FDM and DFT, Pade approximation with Baker’s algorithm is enhanced through introducing multiple frequency search and parabola interpolation. Though Pade approximation is a nonlinear signal processing method and only short time sequence is needed, we find the different length of sequence requirements for 2D and 3D FDTD, which is very important to obtain convergent and accurate results. By using the modified Pade approximation method and 3D FDTD, the 2D slab photonic crystal nanocavity is analyzed and high-Q multimode can be solved quickly instead of large range high-resolution scanning. Monitor position has also been investigated. These results are very helpful to the design of photonic crystal nanocavity devices.     

Polarization squeezing in polarized light

It is shown that polarized light can be polarization squeezed only if it exhibits sub-Poissonian statistics with the Mandel's Q factor less than − 1/2.     

Propagation Rule of Pulsed Light Beams through First-order Optical Systems

1.IntroductionInthepastfe\\'ycarsltllcil1tcnsity-momentsmethodandtheM2factorhavebeenre-vea1edtobeveryuscfulrotlcscribethepropagationlawandthebeamqualityofastaticlightbeam[l~Jj.Rccent1y,1ncji:1sctal.generalizedtheintensitymomentsmethodfortheSCLQ(speetral1y`"el1-centcrcdandlocallyquasi-monochromatic)pulsedlightboms[5j.Itisapparentthatthosercsu]tsubtainedinreferenceL5]areon1yvalidfortheso-calledquasi-monochromaticlightbeamsandarenotvalidforgeneralpolychromaticpulsedlightbeams,esPeciallyaredono…     

Beam quality factor of mixed modes emerging from a multimode step-index fiber

The beam quality factors (or M² parameter) of coherent and incoherent superposition of the several lower-order LP modes emerging from a step-index fiber have been calculated by using the second-order moment method. The results indicate that, for an individual LP mode, the M² parameter takes its maximum value when the normalized frequency V of the step-index fiber approaches the cut-off frequency, and it gradually becomes constant as V increases. In the case of incoherent superposition, the larger the fraction intensity carried by the higher-order mode, the larger the beam quality factor M². Under certain circumstances, the value of the M² parameter of the mixed mode that comprises several LP-modes contents may become even smaller and closer to the ideal Gaussian beam than that of the fundamental mode in a step-index fiber. However, in the case of the coherent superposition, the value of the M² parameter of the mixed mode may be greater than that of the higher-order constituent mode. The results reported here could be helpful for the application of the high-power fiber laser systems.     

Analytical Solution for the Reissner-Sagoci Problem of a Piezoelectric Half-Space

In this paper,a transversely isotropic piezoelectric half-space with the isotropy axis parallel to the z-axis is considered under rotation on a rigid circular disk bonded to the surface of the piezoelectric medium.This is a type of Reissner-Sagoci mixed boundary value problem.By utilizing the Hankel transform,the mixed boundary value problem is simplified into solving a pair of dual integral equations.Full-field analytical expressions for displacement,stresses,and electric displacement inside the half-space are obtained.The shear stresses and electric displacement on the surface are found to be singular at the edge of the rigid circular disk,and the stress intensity factors and electric displacement intensity factor are defined.Numerical results show that material properties and geometric size have significant effects on displacement,shear stresses,and electric displacement.     

椎弓根钉植入针道上骨组织光谱特性研究

运用光谱技术研究了椎骨组织不同位置的特征识别因子.光谱采集系统由双光纤手钻一体式探头(光纤芯径200 μm,中心距离0.5 mm)、卤素光源(波长360～2000 nm)、光纤光谱仪(检测波长为200～1100 nm)和计算机组成,可以同时获得生物组织的漫反射光谱和约化散射系数.以猪椎骨为实验对象,测量椎弓根螺钉植入针道上不同骨组织的漫反射光谱和约化散射系数,并对光谱进行特定波长的峰值、面积、斜率分析,获得特性识别因子.研究发现,椎弓根钉植入针道上不同骨组织的光谱表现出不同的变化特性.其中峰值的变化比约化散射系数的变化高1.88倍,面积的变化比约化散射系数的变化高2.05倍.在495～505 nm处,骨密质和骨疏质的光谱斜率都为正值;在520～535 nm处,骨密质光谱的斜率为正值,而骨疏质光谱的斜率为负值.结果表明,通过光谱特性分析获得的峰值、面积和斜率因子能够有效地区分针道上骨密质与骨疏质的差异.